1. Field of the Invention
The invention pertains to a hydraulic swinging-leaf door drive for swinging doors, the hydraulic drive including an actuating piston, acting on a drive shaft, and a hydraulic pump, connected to the actuating piston by a hydraulic circuit.
2. Description of the Prior Art
Modern hydraulic swinging-leaf door drives are driven by hydraulic units which work with a nearly constant power output. These hydraulic units usually consist of an asynchronous machine, a hydraulic pump (e.g., a gear pump), and a pressure-relief valve. The full hydraulic output, however, is used only during a very short phase of the opening cycle, whereas the excess hydraulic power in the other opening phases is carried away via the pressure-relief valve, so that, as a rule, only about ⅓ of the total hydraulic work produced is used by the swinging-leaf door drive connected to it, whereas the other ⅔ is destroyed via the pressure-relief valve, that is, converted into heat. A flow divider transmission of this type with an open hydraulic circuit containing a pressure-relief valve, however, is unsuitable for a very compact drive, because a motor of large dimensions is required, and such large motors occupy a great deal of space. In addition, because of the poor efficiency of the system, a large amount of lost heat is created, which is difficult to carry away from a compact unit, especially when it is installed under cover.